Secondary oil recovery method

ABSTRACT

Significant improvement in the recovery of hydrocarbons from a subterranean hydrocarbon-bearing formation containing acidsoluble components is accomplished by injecting into the formation via an injection well drilled into a formation communicating with an adjacent producing well and containing acid-soluble components which may or may not have water-sensitive clays and shales included therein, an aqueous acidic solution of an admixture hereinafter described whereupon the acid component reacts with the acid-soluble components of the formation creating passageways or enlarging existing passageways thus facilitating the flow of fluids therein and the admixture prevents post precipitation of dissolved salts and thereby increases the recovery of hydrocarbons from the formation through the adjacent producing well.

United States Patent 1191 Tate Sept. 2, 1975 SECONDARY OIL RECOVERY NIETHOD Primary Examiner-Stephen J. Novosad Assistant ExaminerGeorge A. Suckfield [75] inventor' lack Tate Houston Attorney, Agent, or Firm-T. H. Whaley; C. G. Ries; [73] Assignee: Texaco Inc., New York, N.Y. Jame F, Youn [22] F1led. Dec. 26. 1973 ABSTRACT H PP N061 428,552 Significant improvement in the recovery of hydrocarbons from a subterranean hydrocarbon-bearing forma- 52 11.5. C1 166/271; 166/274 tion Containing acid-Soluble Components is accom- [51] Int 12 21 3 22; 2 3 43 27; plished by injecting into the formation via an injection E215 43/26 well drilled into a formation communicating with an 5 Field f Search 166/271 274 275, 305 R adjacent producing well and containing acid-soluble 166/307, 308 components which may or may not have watersensitive clays and shales included therein, an aqueous [56] References Ci acidic solution of an admixture hereinafter described/ whereupon the acid component reacts with the acid- UNITED STATES PATENTS soluble components of the formation creating passageways or enlarging existing passageways thus facilitat- 3,076 762 2/1963 Dill 166/307 ing the flow of fluids therein and the admixture 3,724,544 4/1973 Tate 166/271 vents post precipitation of dissolved salts and thereby 3,811,505 5/1974 Flournoy cl al. 166/274 increases the recovery of hydrocarbons from the mation through the adjacent producing well.

11 Claims, N0 Drawings SECONDARY OIL RECOVERY METHOD FIELD OF THE INVENTION This invention relates to a method for the recovery of hydrocarbons. from subterranean hydrocarbonbearing formations containing. acid-soluble components in' which the permeability of;the formation communicating between the producing well and adjacent injection well is increasedby treating with an aqueous acidic solution of an admixture as hereinafter described thereby facilitating the flow of fluids through the formation resultingv in increased hydrocarbon recovery via the production well.

DESCRIPTION OF THE PRIOR ART In recovering oil from oil-bearing reservoirs it usually is possible to recover only a minor part of the original oil in place by primary-recovery methods which utilize the naturalforces present in the reservoir. As a result, a variety of supplemental recovery techniques have been utilized to increase the recovery of oil from subterranean hydrocarbon-bearing reservoirs or formations. Although these supplemental techniques are commonly referred toas secondary recovery operations in fact they may be primary or tertiary in sequence of employment. In such techniques, a fluid is introduced-into the formation in order to displace the oil therein to a suitable production system through which the, oil. may be withdrawn to the surface of the earth. Examples of displacing media include gas, aqueous liquids such as fresh water or brine, oil-miscible liquids such as butane, or a water and oil-miscible liquid such as analcohol. Generally, the most promising of the secondary recovery techniques is concerned with the injection into the formation of an aqueous flooding medium either alone or in combination with other fluids.

In the application of these conventional procedures for the production of hydrocarbons from similar formations by the secondary recovery method of waterinjeetion, one of the principal difficulties that has been encountered is the generally low production response realized becauseof the low perineabilities and the consequent low rate of water acceptance of the communicating formation. Thus, these unfavorably low responses both in injection rate and in overall production have led totheabandonment of hydrocarbon production by water-injection methods from many carbonate formations after only a minimal amount of the oil-inplace has been produced.

One of the remedial measures that has been used frequentlyto increase water-injectivity in formations containing aCidQsoluble components is acid-treating of injection wells to improve the permeability surrounding the injection wellbore, and thereby increasing the flow capabilities of the formation in the vicinity of the injection well bore. These measures, however, may result in I only a temporary response in production improvement.

In acidizing an injection well utilizing the commonly employed procedure a non-oxidizing mineral acid, such as hydrochloric acid, is introduced into the injection well, and through the application of sufficient pressure is forced into the adjacent formation, where it reacts with the acid-solublecomponents, particularly the carbonates to dissolvethern to form the respective salt of the acid, carbon dioxide and water. thereby increasing the permeability of the formation adjacent the bore of in the strata or formation which has the desired advantage of opening up passageways into the formation along which the acid can travel to more remote areas from the injection well bore. Conversely, fracturing a formation into which a displacing fluid is injected quite often is not desirable since sweep efficiency may be decreased. The salts formed upon neutralization of the acid are extensively water soluble and may pass through the formation dissolved in the displacing fluid.

There are, however, troublesome complications attending the use of hydrochloric acid, or other similar non-oxidizing mineral acids. In the acidizing process, the following primary beneficial reaction occurs: CaCO 2HCl CaCl H O COJ. Under the higher pressures required to conduct an acidization, the CO is dissolved in the reaction mixture consisting of spent acid and connate water: CO H O H2- CO3 H+ HCO 2H CO The equilibria may be summarized and written:

After acidization is complete, the well is often returned directly to injection, the reaction products of the dissolution being forced into the formation in a solution of the displacing fluid. As the fluid moves away from the well bore, pressure diminishes allowing dissolved gases such as CO to break out of solution, in ducing insoluble carbonates, such as CaCO to postprecipitate.

Similarly, acid-dissolved iron salts may reprecipitate within the formation as hydrous iron oxides a distance from the well bore when pH rises due to exhaustion of the acid. In like manner, gypsum may precipitate if the injected fluid contains sulfate ion and if its temperature increases within the formation since the gypsum has an inverse solubility relationship. Precipitation of this type when it occurs within the capillaries of a tight formation can severely lessen the injection rate by plugging such capillaries.

It is known that molecularly dehydrated polyphosphates, are effective in retarding CaCO precipitation. These polyphosphates are unsatisfactory in the method of the present invention because they undergo rapid hydrolysis in the presence of the mineral acid components. As a result, the scale inhibiting properties of these polyphosphates are destroyed. In addition, one hydrolytic reaction product, the phosphate ion (PO can precipitate with calcium +2 or barium +2 ions present in the produced water, causing additional plugging or scale deposition and they further aggravate acids. In such acidic media they undergo spontaneous depolymerization to an ineffective species. A representative polymeric material which undergoes such hydrolysis in the presence of acids is polyacrylamide. In addition, this polymer has a further disadvantage in that it is unstable in aqueous media at temperatures of about 300F. and upwards. Many Wells that are being treated by the method of the present'invention have bottom hole temperatures of 250300F. or higher.

The chemically altered natural polymers and natural polymers themselves, are effective inhibitors to prevent the precipitation of mineral salts. However, some materials such as sodium carboxymethylcellulose precipitate or decompose in the presence of mineral acids. Other known sequestering agents such as citric or tartaric acids, and/or complexing agents such as ethylenediaminetctraacetic acid and its water-soluble salts are known inhibitors to prevent the deposition of boiler scale in aqueous media. However, such materials are not applicable in the method of the present invention because they are not appreciably surface active and do not adsorb on the formation face.

The primary object of the present invention is to provide a method for the improved recovery of hydrocarbon fluids from subterranean fluid-bearing formations wherein a composition comprising an'aqueous acidic solution of an admixture as hereinafter described is injected into a formation communicating between a producing well and an adjacent injection well, said formation containing acid-soluble components and in some instances also containing water-sensitive clays or shales, and whereafter the acid component of the said composition reacts with the acid-soluble components of the formation to increase permeability of the formation thereby facilitating the flow of fluids therethrough and the admixture component prevents the postprecipitation of compounds formed by the reaction of the acidic component with the formation.

SUMMARY OF THE INVENTION I In accordance with the present invention, there is provided a new and improved method for the recovery of hydrocarbons from subterranean hydrocarbonbearing formations in which there is injected into the formation via an injection well drilled into a-formation communicating with an adjacent producing well and containing acid-soluble components which may or may not have water-sensitive clays included therein, a com position comprising an aqueous acidic solution of an admixture as hereinafter described which is capable of reacting with the acid-soluble components of the formation to increase the permeability and porosity thereof and the admixture component prevents precipitation of compounds formed by the said reaction of the acid component thereby permitting a substantial increase of production of hydrocarbons from the formation via the production well.

An advantage resulting in treating subterranean hydrocarbon-bearing formations having acid-soluble components therein with the aqueous acidic solution of the admixture is that the post-precipitation of aciddissolved salts is prevented or materially decreased. Such post-precipitation, whether it be of carbonates from evolution of CO from solution, hydrous iron oxides from a rise in pH, or of gypsum from an increase in formation temperature, can lead to plugging of formation capillaries and a consequent reduction of permeability. Such an event can reduce injectivity and accordingly the rate of production from adjacent wells.

DESCRIPTION OF THE INVENTION The method of the present invention in its broadest embodiment comprises introducing via an injection well drilled into a hydrocarbon-bearing formation containing acid-soluble components and communicating with a producing well a fluidcomposition comprising an aqueous acidic solution of an admixture as hereinafter described in amounts sufficient to react with the formation so as to increase substantially the flow capability of the formation and to thereafter produce hydrocarbons from the said subterranean formation at an increased rate through the production well.

The admixture useful in preparing the aqueous acidic solution of the present invention is formed from about one part by weight of a sulfated/sulfonated polyethoxy alkyl phenol containing from about 8 to about l4 carbon atoms in the alkyl group and from about 4 to about 10 ethoxy groups, together with from about 1 to 3 parts by weight of a C -C alkyl benzene sulfonic acid, including the alkali metal and ammonium salts of one or both compounds, as well as mixtures thereof.

Representative sulfated/sulfonated polyethoxy alkyl phenols include the octyl-, nonyl-, decyl-, undecyl-, dodecyl-, tridecyland tetradecyl-phenols ethoxylated with about 4 to about 10 ethoxy groups, such as the tetraethoxy-, hexaethoxy-, octaethoxyand decaethoxy adducts of the above nonyl phenols, the ammonium, sodium and potassium salts thereof. Particularly preferred compounds are sulfated/sulfonated tetraethoxylated nonyl phenol, sulfated/sulfonated hexaethoxylated nonyl phenol, and sulfated/sulfonated nonyl phenol containing an average of about 9.5 ethoxy groups therein.

Representative alkyl benzene sulfonic acids, including the straight and branched chain alkyl groups, useful in the practice of the'inventio n include the octyl-, nonyl-, decyl-, undecyl-, dodecyl-, tridecyland tetradec yl-benzene sulfonic acids, the corresponding sodium, potassium and ammoniurn salts thereof as well as mixtures of one or more of said compounds. A preferred group is the C -C alkyl benzene sulfonic acids and the above salts thereof. I

As used in the present specification and claims the expression sulfated/sulfonated polyethoxy alkyl phenol refers to the reactionproduct'of a polyethoxy alkyl phenol described hereinabove with chlorosulfonic acid or sulfur trioxide for a time period of from about 5 to 90 minutes at a temperature in the range of from about 50 to 60C., using a reactant mole ratio of from about one mole of said phenol per 0.8 to 1.3 mole of said chlorosulfonic acid or sulfur trioxide.

Analysis of the resulting reaction products showed that from about to percent thereof was sulfated while the 10 to 30 percent remaining was sulfonated. Accordingly, the term sulfated/sulfonated was used to describe this reaction product.

A preferred set of reaction conditions are from about 55 to about 60C., 30 to 90 minutes in time and mole ratios of from about one mole of said phenol per l-1.3

mole of the chlorosulfonic acid or sulfur trioxide.

A preferred ratio of the admixture components is about one part by weight of the sulfated/sulfonated polyethoxy alkyl phenol to from about 1.25 to 2.75

parts by weight of the C C alkyl benzene sulfonic acid.

Preferably. the acidic aqueous treating composition of this invention injected into the hydrocarbon-bearing formation comprises an aqueous solution of from about 0.01 to about 5 percent. preferably 1 to 3 percent by weight of carbon dioxide and which contains therein between from about 0.005 to about 1 percent by weight, preferably from about 0.05 to about 0.5 percent of the aforesaid admixture.

In the first step of preparing the aqueous acidic com position of this invention, a solution containing from about 0.01 to about 5 percent by weight of carbon dioxide in water is prepared. The required amount of the admixture is then admixed with the aqueous acid solution.

The method of this invention can be carried out with a wide variety of injection and production systems which will comprise one or more Wells penetrating the producing strata or formation. Such wells may be catcd and spaced in a variety of patterns which are well-known to those skilled in the art. For example, the so-called line flood pattern may be used, in which case the injection and producing systems are composed of rows of wells spaced from one another. The recovery zone, i.e., that portion of the producing formation from which hydrocarbons are displaced by the drive fluid to the production system, in this instance will'be that part of the formation underlying the area between the spaced rows. Another pattern which is frequently used is the so-called circular flood in which the injection system comprises a central injection well while the production system comprises a plurality of production wells spaced about the injection well. Likewise, the injection and production systems each may consist of only a single well and here the recovery zone will be that part of the producing strata underlying an elliptical-like area between the two wells which is subject to the displacing action of the aqueous drive fluid. For a more elaborate description of such recovery patterns reference is made to Uren, L. C., Petroleum Production Engineering-Oil Field Exploitation, Second Edition, McGraw Hill Book Company, Inc., New York, 1939, and to U.S. Pat. Nos. 3,472,318 and 3,476,182.

In carrying out the method of this invention, the aqueous acidic solution of the admixture is forced, usually via a suitable pumping system, down the well bore of an injection well and into the producing formation through which it is then displaced together with hydrocarbons of the formation in the direction of a production well. As those skilled in the art will readily understand, the pressure employed is determined by the nature of the formation, viscosity of the fluid, and other operating variables. The method of this invention may be carried out at a pressure suffi eient merely to penetrate the formation or it may be of sufficient magnitude to overcome the weight of the overburden and create fractures in the formation. Propping agents. to prop open the fractures as created, for example to 60 mesh sand, in accordance with known fracturing procedures, may be also employed with the aqueous acidic solution containing the admixture.

The formation may be treated continuously with the resulting solution or such treatment may be temporary. If desired, however, after a time. conventional flooding may be resumed. The aqueous acidic solution of admixture also may be applied in a modified water flood operation in which there is first injected into the well bore a slug of the aqueous acidic solution of admixture which is forced under pressure into the subterranean formation. This first step is then followed by a similar injection step wherein a slug of an aqueous drive fluid, such as water, is injected, which is thereafter followed by a repetition of the two steps. This sequence may be repeated to give a continuous cyclic process. The size of the slugs may be varied within rather wide limits and will depend on a number of conditions, including the thickness of the formation, its characteristics and the conditions for the subsequent injection of the aqueous drive medium.

In the method of this invention, the admixture component of the composition provides means whereby ions produced by the reaction of the acid component with the formation having tendencies to precipitate as salts such as CaCO,,, hydrous iron oxide and CaSO .2- H O combine with the admixture moiety to form a highly stable complex therewith so that solid calcium carbonate does not precipitate from the spent treating solution. This binding up of the aforementioned calcium ions from weakly ionizable compounds permits the formed complex to remain dissolved in the treating solution and pass through the formation pores. Further, the admixture component of the composition provides means whereby the nucleation and growth of the solid itself is thwarted, so that solid salts do not precipitate from the spent treating solution. Finally, the admixture component of the composition provides means whereby continuous protection against postprecipitation of salts is obtained for a considerable period of time subsequent to treatment due to continuous slow desorption of the component from the formation faces. In contrast, use of surfactants having merely dispersant and suspending properties and not possessing the capability of molecularly binding up these produced ions or thwarting the nucleation and growth of solid salts thereof will permit post-precipitation of said salts from such treating solution with the likelihood of plugging up the formation passageways during subsequent recovery of desirable formation hydrocarbons therethrough.

It should be understood that the concentrations of the admixture and the acid component of the composition are chosen to provide a displacing fluid of the desired rhelogical properties. Similarly, the appropriate admixture is selected on the basis of the formation being treated as well as other operating conditions employed.

The method of the present invention also finds applicability in combination with subsequent treatment of the formation using a polymeric mobility control agent in aqueous solution introduced therein through an injection well to minimize viscous fingering and to enhance volumetric sweep efficiency. Suitable mobility control agents are well known in the art such as the hydrophilic polymers of the polyacrylamides or the polysaccharides which can be used in amounts of from about 0.01 to about 0.1 percent by weight.

The method can be varied to employ injection of a large slug of the aqueous acidic solution of the admixture followed by the aqueous solution of the polymeric mobility control agent, then followed by water injection. Repetitive treatments of one or all of these steps are within the purview of the invention. Additionally and/or optionally one may inject gaseous carbon dioxide after any or all of these slug treatments, to impart enhanced mobility to the oil by decreasing its viscosity, through the injection well.

Following is a description by way of example of a method for carrying out the method of the present invention.

EXAMPLE I Through a water injection well drilled into a limestone formation there is displaced under pressure down the tubing and into the formation an aqueous acidic solution containing 1 percent by weight of carbon dioxide and 1 percent by weight of an admixture consisting of a 1/1 ratio of sulfated/sulfonated tetraethoxy nonyl phenol and ammonium dodecyl benzene sulfonate. The pressure required to inject the required volume of water declines considerably and no increase in said pressure is noted subsequent to treatment, indicating that post precipitation of CaCO within the formation leading to permeability reduction is prevented or materially lessened. The well is then returned to conventional water injection. After about 30 days the production of hydrocarbons from an adjacent producing well is substantially increased.

EXAMPLE II A flooding operation is carried out in an oilcontaining reservoir in accordance with the process of this invention. Four injection wells are arranged in a rectangular pattern around a single centrally located production well in this system. A slug consisting of 75 barrels of an aqueous acidic solution containing 2 percent by weight of carbon dioxide and 0.75 percent by weight of the same admixture as Example I is displaced via each of the four injection wells into the formation at a rate of about 50 bbl/day. In the next step, 100 barrels of water are injected under pressure into the producing formation through each injection well at a rate of about 55 bbl/day. This sequence of operations is re peated numerous times and the result is an increased injection rate of the drive streams into the injection wells and a subsequent increase in the rate of production of hydrocarbons via the production well.

EXAMPLE III An injection well in a formation containing about 30% HCl soluble material is treated with 1,500 gallons of aqueous carbon dioxide containing 0.5 percent by weight of an admixture consisting of sulfated/sulfonated nonyl phenol ethoxylated with about 9.5 ethylene oxide groups and sodium decyl benzene sulfonate in a 1/1 weight ratio. The aqueous acidic admixture is displaced from the tubing into the formation with lease water and the well shut in for 24 hours. Thereafter the well is returned to water injection. The injectivity of the well is materially increased for a sustained period of time resulting in enhanced hydrocarbon recovery.

It is significant that the admixture is an effective material in the presence of high calcium ion concentrations of the order of up to 10,000 ppm or more, for the sulfated/sulfonated polyethoxy alkyl phenols are relatively ineffective at these high calcium ion concentrations and the alkyl benzene sulfonic acids alone are not satisfactory at calcium ion concentrations above about 50 ppm. The admixture appears to stabilize the alkyl benzene sulfonic acid component.

Obviously, many modifications and variations of the invention as hereinabove set forth may be made without departing from the. spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

I claim:

1. A method for the recovery of hydrocarbons from a hydrocarbon-bearing formation containing acidsoluble components having at least one injection well and at least one production well penetrating the said formation and in fluid communication, which comprises displacing through the formation a composition comprising an aqueous acid solution formed from about 0.01 to about 5 percent by weight of carbon dioxide and from about 0.0005 to about 1 percent by weight of an admixture therein, said admixture being formed from about one part by weight of(A) a member selected from the group consisting of a sulfated/sulfonated polyethoxy alkyl phenol containing from about 8 to about 14 carbon atoms in the alkyl group and from about 4 to about 10 ethoxy groups, the corresponding alkali metal and ammonium salts and mixtures thereof, with (B) from about 1 to about 3 parts by weight of a member selected from the group consisting of a C C alkyl benzene sulfonic acid, the corresponding alkali metal and ammonium salts and mixtures thereof.

2. Method as claimed in claim 1 wherein said admixture is present in said aqueous acidic solution in an amount of from about 0.05 to about 0.5 percent by weight.

3. Method as claimed in claim 1 wherein said admixture is formed from about 1 part by weight of said sulfated/sulfonated polyethoxy alkyl phenol to from about 1.2 to 2.75 parts by weight of said C,,C alkyl benzene sulfonic acid.

4. Method as claimed in claim 1 wherein said admixture is composed of sulfated/sulfonated tetraethoxy nonyl phenol and ammonium dodecyl benzene sulfonate.

5. Method as claimed in claim 1 wherein said admixture is composed of sulfated/sulfonated hexaethoxy nonyl phenol and sodium decyl benzene sulfonate.

6. Method as claimed in claim 1 wherein said admixture is composed of sulfated/sulfonated octaethoxy nonyl phenol and ammonium dodecyl benzene sulfonate.

7. Method as claimed in claim 1 wherein said admixture is composed of sulfated/sulfonated polyethoxy nonyl phenol wherein the average number of ethoxy groups therein is about 9.5, and sodium decyl benzene sulfonate.

8. Method as claimed in claim 1 wherein said carbon dioxide is present in an amount of from about 1 to about 3 percent by weight.

9. Method as claimed in claim 1 wherein said solution is injected down the injection well bore penetrating said formation under a pressure greater than the formation pressure and sufficient to create fractures in the formation.

10. Methodas claimed in claim 1 wherein said solution is injected down the well bore penetrating said for mation under a pressure greater than formation pres sure but less than the pressure required to create fractures in the formation. I i

11. A method for the recovery of hydrocarbons from a hydrocarbon-bearing formation containing acidsoluble-components and having at least one injection l() ethoxy groups, the corresponding alkali metal and ammonium salts and mixtures thereof. with (B) from about I to about 3 parts by weight of a member selected from the group consisting of a C C alkyl benzcne sulfonic acid, the corresponding alkali metal and ammonium salts and mixtures thereof, thereafter injecting a slug of an aqueous drive fluid into the formation to drive the said composition through said formation toward said production well and recovering hydrocarbons through the production well.

* l= l l 

1. A METHOD FOR THE RECOVERY OF HYDROCARBONS FROM A HYDROCARBON-BEARING FORMATION CONTAINING ACID-SOLUBLE COMPONENTS HAVING AT LEAST ONE INJECTIONN WELL AND AT LEAST ONE PRODUCTION WELL PENETRATING THE SAID FORMATION AND IN FLUID COMMUNICATION, WHICH COMPRIES DISPLACING THROUGH THE FORMATION A COMPOSITION COMPRISING AN AQUEOUS ACID SOLUTION FORMED FROM ABOUT 0.01 TO ABOUT 5 PERCENT BY WEIGHT OF CARBON DIOXIDE AND FROM ABOUT 0.0005 TO ABOUT 1 PERCENT BY WEIGHT OF AN ADMIXTURE THEREIN, SAID AMIXTURE BEING FORMED FROM ABOUT ONE PART BY WEIGHT OF (A) A MEMBER SELECTED FROM THE GROUP CONSISTING OF A SULFATED/SULFONATED POLYETHOXY ALKYL PHENOL CONTAINING FROM ABOUT 8 TO ABOUT 14 CARBON ATOMS IN THE ALKYL GROUP AND FROM ABOUT 4 TO ABOUT 10 ETHOXY GROUPS, THE CORRESPONDING ALKALI METAL AND AMMONIUM SALTS AND MIXTURE THEREOF, WITH (B) FROM ABOUT 1 TO ABOUT 3 PARTS BY WEIGHT OF A MEMBER SELECTED FROM THE GROUP CONSISTING OF A C8-C14 ALKYL BENZENE SULFONIC ACID, THE CORRESPONDING ALKALI METAL AND AMMONIUM SALTS AND MIXTURES THEREOF.
 2. Method as claimed in claim 1 wherein said admixture is present in said aqueous acidic solution in an amount of from about 0.05 to about 0.5 percent by weight.
 3. Method as claimed in claim 1 wherein said admixture is formed from about 1 part by weight of said sulfated/sulfonated polyethoxy alkyl phenol to from about 1.2 to 2.75 parts by weight of said C8-C14 alkyl benzene sulfonic acid.
 4. Method as claimed in claim 1 wherein said admixture is composed of sulfated/sulfonated tetraethoxy nonyl phenol and ammonium dodecyl benzene sulfonate.
 5. Method as claimed in claim 1 wherein said admixture is composed of sulfated/sulfonated hexaethoxy nonyl phenol and sodium decyl benzene sulfonate.
 6. Method as claimed in claim 1 wherein said admixture is composed of sulfated/sulfonated octaethoxy nonyl phenol and ammonium dodecyl benzene sulfonate.
 7. Method as claimed in claim 1 wherein said admixture is composEd of sulfated/sulfonated polyethoxy nonyl phenol wherein the average number of ethoxy groups therein is about 9.5, and sodium decyl benzene sulfonate.
 8. Method as claimed in claim 1 wherein said carbon dioxide is present in an amount of from about 1 to about 3 percent by weight.
 9. Method as claimed in claim 1 wherein said solution is injected down the injection well bore penetrating said formation under a pressure greater than the formation pressure and sufficient to create fractures in the formation.
 10. Method as claimed in claim 1 wherein said solution is injected down the well bore penetrating said formation under a pressure greater than formation pressure but less than the pressure required to create fractures in the formation.
 11. A method for the recovery of hydrocarbons from a hydrocarbon-bearing formation containing acid-soluble components and having at least one injection well and at least one production well penetrating the said formation in fluid communication, which comprises displacing through the formation a slug of an aqueous acidic solution formed from about 0.01 to about 5 percent by weight of carbon dioxide containing therein from about 0.005 to about 1% by weight of an admixture, said admixture being formed from about one part by weight of (A) a member selected from the group consisting of a sulfated/sulfonated polyethoxy alkyl phenol containing from about 8 to about 14 carbon atoms in the alkyl group and from about 4 to about 10 ethoxy groups, the corresponding alkali metal and ammonium salts and mixtures thereof, with (B) from about 1 to about 3 parts by weight of a member selected from the group consisting of a C8-C14 alkyl benzene sulfonic acid, the corresponding alkali metal and ammonium salts and mixtures thereof, thereafter injecting a slug of an aqueous drive fluid into the formation to drive the said composition through said formation toward said production well and recovering hydrocarbons through the production well. 